1. Field of the Invention
The present invention generally relates to anode used in a marine environment and, more particularly, to an anode which is made of a polymer material, such as vinyl ester, that is impregnated with conductive particles, such as graphite powder.
2. Description of the Prior Art
It is well known that submersible components can suffer corrosion degradation as a result of galvanic currents between dissimilar metals. This type of galvanic corrosion can severely damage marine components, such as drive units. As an example, since the propeller of a marine propulsion system and the submerged housing of that same system are often made of dissimilar metals, a galvanic reaction can easily occur. This can result in severe damage to the marine drive unit.
U.S. Pat. No. 4,322,633, which issued to Staerzl on Mar. 30, 1982, discloses a marine cathodic protection system. The system maintains a submerged portion of a marine drive unit at a selected potential to reduce or eliminate corrosion thereto. An anode is energized to maintain the drive unit at a preselected constant potential in response to the sensed potential at a closely located reference electrode during normal operations. Excessive current to the anode is sensed to provide a maximum current limitation. An integrated circuit employs a highly regulated voltage source to establish precise control of the anode energization.
U.S. Pat. No. 4,528,460, which issued to Staerzl on Jul. 9, 1985, discloses a cathodic protection controller. A control system for cathodically protecting an outboard drive unit from corrosion includes an anode and a reference electrode mounted on the drive unit. Current supplied to the anode is controlled by a transistor, which in turn is controlled by an amplifier. The amplifier is biased to maintain a relatively constant potential on the drive unit when operated in either fresh or salt water.
U.S. Pat. No. 4,492,877, which issued to Staerzl on Jan. 8, 1985, discloses an electrode apparatus for cathodic protection. The apparatus is provided for mounting an anode and reference electrode of a cathodic protection system on an outboard drive unit. The apparatus includes an insulating housing on which the anode and reference electrode are mounted and a copper shield mounted between the anode and the electrode to allow them to be mounted in close proximity to each other. The shield is electrically connected to the device to be protected and serves to match the electrical field potential at the reference electrode to that of a point on the outboard drive unit remote from the housing.
U.S. Pat. No. 6,183,625, which issued to Staerzl on Feb. 6, 2001, discloses a marine galvanic protection monitor. The system uses to annunciators, such as light emitting diodes, to alert a boat operator of the current status of the boat's galvanic protection system. A reference electrode is used to monitor the voltage potential at a location in the water and near the component to be protected. The voltage potential of the electrode is compared to upper and lower limits to determine if the actual sensed voltage potential is above the lower limit and below the upper limit. The two annunciator lights are used to inform the operator if the protection is proper or if the components to be protected is either being over protected or under protected.
U.S. Pat. No. 3,953,742, which issued to Anderson et al on Apr. 27, 1976, discloses a cathodic protection monitoring apparatus for a marine propulsion device. The system monitor is coupled to an impressed current cathodic protection circuit used for corrosion protection circuit used for corrosion protection of a submerged marine drive. The cathodic protection circuit includes one or more anodes and a reference electrode mounted below the water line and connected to an automatic controller for supplying an anode current which is regulated in order to maintain a predetermined reference potential on the protected structure. A switch selectively connects a light emitting diode lamp or other light source between the controller output and ground so that the controller may, when tested, be used to operate the light source in order to confirm that power is available to the anode.
U.S. Pat. No. 6,251,308, which issued to Butler on Jun. 26, 2001, describes a highly conductive molding compound and fuel cell bipolar plates comprising the compounds. A conductive polymer is disclosed which is suitable for use in applications which require corrosion resistance including resistance to corrosion when subjected to acidic flow at temperatures ranging from −40 degrees Fahrenheit to 140 degrees Fahrenheit and which can be molded into highly intricate and thin specimens which exhibit consistent conductivity, sufficient strength and flexibility, and appropriate surface characteristics. In particular the invention involves molding unsaturated prepolymer resin composition which have high loadings of conductive fillers. Further to enable the necessary characteristics, the composition includes rheological modifies such as Group II oxides and hydroxides; carbodiamides; aziridines; polyisocyanates; polytetrafluroetheryle (PTFE); perfluoropolyether (PFPE), and polyethylene. Ostensibly, these modifiers act to alter the apparent molecular weight and three dimensional prepolymer network structures correcting rheological deficiencies which otherwise lead to excessive resin particulate separation during the molding process and large variances in bulk conductivity across the plate surface. The composition is disclosed for use in electrochemical cells, such as fuel cells.
U.S. Pat. No. 6,365,069, which issued to Butler et al on Apr. 2, 2002, describes a process of injection molding highly conductive molding compounds and an apparatus for this process. A technique and apparatus are disclosed for injection molding highly filled conductive resign compositions. These compositions include one or more unsaturated polyester and vinyl ester resin; a copolymer having a terminal ethylene group; and at least about 50 weight percent of an inorganic particulate conductive filler, an initiator, and a rheological modifier to prevent phase separation between the resin and the conductive filler during molding. The method allows these compositions to be molded into highly intricate and thin electrically and thermally conductive specimens without significant post process machining. The method involves the use of an injection molding apparatus that has a hopper with an auger having a vertical component in its positioning to feed into the feed throat of an injection molding machine which has a phenolic screw that has been modified to have a constant inner diameter and a constant flight depth.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
The material described in U.S. Pat. Nos. 6,251,308 and 6,365,069 have been used in certain devices, such as fuel cells. The high electrical conductivity of the material and its resistance to corrosive elements allows it to be used as a conductive material in certain environments that would otherwise attack many other types of material. The material is available in commercial quantities from Quantum Composites, Inc. which is a subsidiary of Premix, Inc. One such material is referred to as “Pemtex”.
Marine anodes have been made from expensive materials, such as platinum and titanium, in order to provide a useful life when they are submerged for use as an anode in a cathodic protection system. It would be useful if a marine anode could be made of a less expensive material that can withstand rough treatment in a corrosive environment.